A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus may be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which may be referred to as a mask or a reticle, may be used to generate a pattern corresponding to an individual layer of a flat panel display (or other device). This pattern may be transferred on (part of) the substrate (e.g. a glass plate), e.g. via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
The patterning device may be used to generate various patterns, for example a color filter pattern, or a matrix of dots. Instead of a mask, the patterning device may comprise a patterning array that comprises an array of individually controllable elements. An advantage of such a system compared to a mask-based system is that the pattern can be changed more quickly and for less cost.
A flat panel display substrate may be rectangular in shape. Lithographic apparatus designed to expose a substrate of this type may provide an exposure region which covers a full width of the rectangular substrate, or which covers a portion of the width (for example half of the width). The substrate may be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through the beam of radiation. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure may be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate may be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
The use of an immersion liquid between the projection system and the substrate has been suggested for use in a conventional lithography apparatus with a mask. Because the refractive index of the immersion liquid is greater than that of, for example, air, it may be possible to image smaller features on the substrate than when, for example, air is between the projection system and the substrate.